Conventionally, a relatively large opening is provided to a side part of a vehicle such as for example station wagon and minivan, and allows an occupant to easily get on and off the vehicle via the opening, or allows a baggage to be put in and taken out of the vehicle via the opening. This opening is opened and closed with a sliding door (opening and closing unit) provided with a roller assembly. Since the sliding door is heavy in weight, the vehicle equipped with the sliding door is provided with a sliding door opening and closing mechanism capable of automatically opening and closing the sliding door.
The sliding door opening and closing mechanism is provided with a guide rail, thereby rolling the roller assembly along the guide rail to guide the sliding door. This guide rail extends in a longitudinal direction of the vehicle, and it is disposed in the vicinity of the opening. The guide rail is provided with a pull-in portion disposed on the front side of the vehicle and curved inward from the side part of the vehicle, and therefore, the sliding door is drawn into the opening so as to reach a fully-closed state just before the sliding door fully close the opening.
Pulleys for changing the direction of cables for pulling the sliding door in an opening direction and in a closing direction are respectively provided to a front side and a rear side of the guide rail. An end of each cable changed in direction is wound around a drum of a driving unit. The driving unit is driven so as to move the cables by rotating the drum in clockwise and counterclockwise directions, thereby pulling the sliding door in the opening direction or the closing direction.
For example, Japanese Patent Application Laid-Open Publication No. 2002-227944 (FIG. 1) discloses a technique (cable driving device) known as a sliding door opening and closing mechanism. The cable driving device described in Japanese Patent Application Laid-Open Publication No. 2002-227944 (FIG. 1) is provided with: an actuator (driving unit) which has an electric motor (driving source); and a drum which is rotated clockwise and counterclockwise by the electric motor. When the sliding door is opened and closed manually without being driven by the electric motor, the electric motor is rotated depending on the rotation of the drum.